Conventional refrigerated automotive air conditioners operate on the high pressure system wherein a mechanical compressor compresses the refrigerant which then passes through a condenser where the heat passes from the refrigerant to the outside air to thus condense the high pressure gas into a high pressure liquid. After passing through a receiver drier, the high pressure liquid passes then through an expansion valve to thus pass low pressure liquid through the evaporator, where the low pressure liquid extracts the heat from the air passing over the evaporator to thus cool the air which is then discharged into the interior of the motor vehicle. The low pressure gas from the evaporator then passes to the compressor where it is again compressed whereby the heat which is taken up by the evaporation of the liquid into the gas in the evaporator is then discharged into the ambient air during the condensing of the high pressure gas into the high pressure liquid form.
These conventional refrigerated air conditioners have to have a high capacity in order to adequately cool the heat load of the interior of the vehicle, and often this requires that power in the order of 15 horse power is often required to effectively cool the vehicle.
A great deal of work has been carried out in order to increase the efficiencies of such refrigerated air conditioners, and it has now been found that the efficiency of the air conditioner can be effectively improved and thus the power load on the driving motor which is drawn by the compressor would be greatly reduced.
In this respect it has been found that the refrigerant after passing through the evaporator has not been completely vaporized, and the fluid issuing therefrom is a mixture of liquid and vapour. Also the high pressure liquid entering the expansion valve is often at a relatively high temperature, and if the liquid on entry to the expansion valve and also to the evaporator is of a lower temperature than a greater cooling effect to the air flowing over the evaporator would take place due to the fact that more heat has to be extracted from the air in order to vaporize the liquid.
Also with such systems the receiver/drier requires periodic maintenance, and it is common practice to replace the receiver/drier whenever recharging has to be carried out. Also replacement of the unit must take place whenever the screens in the receiver/drier become clogged, or when the desiccant in the unit is saturated and cannot absorb any more moisture.
The efficient operation of the receiver/drier depends to a large extent upon its temperature, for the capacity of the desiccant to hold the moisture decreases as its temperature increases.
Hence if the receiver/drier is kept as cool as possible, or is cooled, then its efficiency increases.